Wireless service providers that offer voice over internet protocol (VOIP) and push-to-talk (PTT) services are starting to move these and other real-time applications and services to a converged evolution-data optimized (EV-DO) based radio access network (RAN) from their current 1X based radio access network. All the signaling messages for an idle access terminal (AT) in an EV-DO based RAN go through a ControlChannel (CC) and are transmitted across many sectors. For example, a RouteUpdateRequest message sent by the access network (AN) to the entire radio network controller's (RNC) coverage area for finding an AT's current location which may be followed by the AN sending another message such a DOS (data over signaling) message to several sectors in which the AT has good pilot signal strength. The DOS message may carry call-setup related information or an instance short message, once the access terminal returns the requested RouteUpdate message. Traditional paging strategy sends a page message to a last seen active-set in a first attempt to contact the access terminal, escalates to an entire RNC's coverage area in the next attempt, and is followed with a page to an RNC group that combines a few adjacent RNCs. For RNCs with about 50-cells/150-sectors, nearly 50 sectors on average may be involved in transmitting page messages for each call, assuming a 70%-75% success rate for the first attempt and 24%-29% for the second attempt within RNC, and just 1% for the third attempt to the RNC group. The success rate of the attempts to page the access terminal are a good indication of overall average response time for call setup within the RAN. One way to improve the success rate for the first page (it is only about 60%-80% for this traditional page strategy) is to page the entire 150 sectors in the RNC in the first attempt. However, this may use too large of an amount of network resources during a busy hour for an EVDO based RAN since it does not have a dedicated paging channel which is the case for the 1X based RAN.
It is desirable to reduce a response time for real-time applications (e.g., using data over signaling, DOS). However, in the EVDO RAN, the CC can transmit no more than 16 bytes of physical layer data in each time-slots at its highest rate of 76.8 kbps. Accordingly, a 100 byte general ‘compressed SIP invite’ (call-setup message) will take 7 times-slots for the CC to transmit. Since an EVDO based RAN delivers high-speed service based on its high-speed traffic/broadcast channels, time-slots used by the slower control channels will degrade the overall system performance.
At 1.2K busy hour call attempts (BHCA) per sector (35Erlang with 100 seconds hold time) for EVDO based RAN, a RNC with 50-cells/150-sectors will transmit more than 5 page messages per ControlChannelCycle (CCcycle) from every sector, assuming the traditional paging strategy is performed. It will be approximately 20-25 page messages per CCcycle if the entire RNC coverage area is paged at the first attempt for better result as it is often the customary way for 1X based RAN. With this rate, the system simply cannot afford to convert some of the page messages to DOS messages (data over signaling) for passing the call-setup information directly to the users as the real-time applications (such as PTT services) would like to do.
Using a zone base method for tracking users (e.g., using the RouteUpdateTriggerCode for zones as small as one or a few sectors) will limit the number of sectors participating for transmitting signaling messages so that some CC cycles can be saved from air interface resources. But for small zones, access terminals that are approximately stationary near the zone boundaries could often “ping-pong” between the zones as they are toggling between sectors that belong to different zones. In this case, while some CC cycles have been saved, it places an additional load on the Access Channels (AC), which could be very heavy such that the overall system's accessing ability will be impacted.
Thus, a need exists for an increase in signaling performance and efficient use of air interface resources.